Background: Environmental tobacco smoking (ETS) significantly contributes to morbidity and mortality and is a known risk factor for lung cancer development in lifelong nonsmokers. The metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its glucuronides (NNAL-Glucs) have now emerged as leading biomarkers for the study of carcinogen exposure in non-smokers exposed to ETS. Materials and Methods: We carried out our study on NNAL in the urine of non-smokers exposed to ETS and the association between ETS and lung cancer. Subjects were enrolled from 2008-2010. NNAL was analyzed for 74 non-smoking lung cancer and 85 healthy controls. The main objective of this study was to provide an estimate of the risk of lung cancer from exposure to ETS in the Korean population. Results: The mean NNAL concentration in urine was significantly lower in non-smoking patient groups (n=74) than in control groups (n=85) ($4.7{pm}15.0$ pg/mg, $6.5{pm}17.9$ pg/mg, respectively, Mann-Whitney U test, p<0.001). Conclusions: The urine NNAL of non-smoking patients with lung cancer was not elevated with regard to the non-smoking control group. This may be due to life-style changes after diagnosis. A prospective study will be needed to evaluate the association of NNAL and non-smoking lung cancer.